Process for the preparation of groundwood pulp from a dicotyledonous plant

ABSTRACT

There is disclosed a process for the preparation of groundwood or mechanical pulp from a dicot material such as kenaf. The process as applied to kenaf comprises treating chopped kenaf at about atmospheric pressure and ambient temperature with an aqueous solution of alkaline sulfite and sodium carbonate at a pH of from about 10 to 11 for about 1-30 minutes, and thereafter mechanically refining said material to form a pulp.

United States Patent 2,749,241 6/1956 Marpillero Walter P. Lawrence Hamilton, Ohio June 23, 1969 Nov. 16, 1971 U. S. Plywood-Champion Papers, Inc. New York, N.Y.

lnventor Appl. No. Filed Patented Assignee PROCESS FOR THE PREPARATION OF GROUNDWOOD PULP FROM A DICOTYLEDONOUS PLANT 7 Claims, No Drawings Reierences Cited UNITED STATES PATENTS Kenaf Composition,"

OTHER REFERENCES Nieschlag et al., A Search For New Filber Crops, 1V: TAPPl, VoL 44, No. 7, 7- 1961, 162-99.

Clark et al., A Search For New Fiber Crops, V: "Pulping Studies On Kenaf, TAPPl, Vol. 45, No l0, 10- 1962 (62- 99) Primary Examiner-S. Leon Bashore Assistant Examiner-Arthur L. Corbin Attorney-Roylance, Abrams, Berdo & Kaul ABSTRACT: There is disclosed a process for the preparation of groundwood or mechanical pulp from a dicot material such as kenaf. The process as applied to kcnaf comprises treating chopped kenaf at about atmospheric pressure and ambient temperature with an aqueous solution of alkaline sulflte and sodium carbonate at a pH of from about 10 to 11 for about l-30 minutes, and thereafter mechanically refining said material to form a pulp.

PROCESS FOR THE PREPARATION OF GROUNDWOOD PULP FROM A DICOTYLEDONOUS PLANT This invention relates to the preparation of groundwood or mechanical pulp from a dicotyledonous plant. More particularly, this invention relates to the treatment of kenaf to prepare a groundwood or mechanical pulp suitable for use in the manufacture of paper.

The use of groundwood or mechanical pulp in the manufacture of paper is well known. Both coniferous and deciduous species of wood are commonly used for the production of groundwood pulp. However, the scarcity and the cost of woods which are particularly suited for specific types of groundwood have promoted searches for alternative raw materials. For example, the treatment of monocots such as sugar cane bagasse, straw and various types of grasses with sodium sulfite over a wide pH range to prepare a pulp which be used in the preparation of paper has been suggested. The light color of the central woody system of kenaf, which comprises about 70 percent of the stalk weight, makes it a possible candidate for groundwood. However, kenaf is quite sensitive to alkalinity.

It is an object of this invention to produce a mechanical or groundwood pulp from a dicotyledonous plant such as kenaf.

It is another object of this invention to treat kenaf so as to induce fibrillation and to reduce chop in the subsequent grinding operation.

These and other objects are attained by the practice of this invention which, briefly, comprises treating a dicotyledonous plant with an aqueous solution of an ammonium, alkali metal or alkaline earth metal sulfite and sodium carbonate, said solution having a pH of from about 7 to 11.5 and, preferably from about 10 to 11, for from about 1-30 minutes. .The solution which is used to treat the dicotyledonous plant material should contain from about 1-10 percent by weight of sodium sulfite and from about 1- percent by weight of sodium carbonate, these weights being based on the dry weight of the kenaf. The treated material is then refined to form a groundwood or mechanical pulp by conventional techniques.

Dicotyledonous plants which may be used in the practice of this invention include kenaf, crotalaria, roselle and other members of the hibiscus family, in a chopped form. Also, there may be used tree sprouts or saplings, including twigs or bark, from hardwood trees such as cottonwood, eucalyptus, or sycamore.

The invention will be more fully described hereinafter with particular reference to kenaf, which is the preferred dicotyledonous plant used in the practice of this invention.

Kenaf is a dicotyledonous plant and as such contains cambium, xylem, phloem, etc. Xylem is comprised of tracheids, vessels, rays, etc., which provide the desirable raw materials for paper. Monocots, on the other hand, such as wheat straw, rice straw, sugar cane, corn, sorghum, bamboo, etc., contain no tracheids, vessels, etc.

The kenaf which is used in the practice of this invention may be whole kenaf plants, either green or aged and desiccated. The invention has particular advantages when applied to aged kenaf. Before treatment with the alkaline sulfite, the kenaf is chopped into pieces about one-fourth to inches long and, preferably, 2 to 3 inches long. The pieces of kenaf may then be soaked in water to moisten them.

Chopped kenaf is treated with the aqueous solution of sulfite and sodium carbonate, preferably at atmospheric pressure and ambient temperature to uniformly wet the pieces. While sodium sulfite is the preferred alkaline sulfite used, other sulfitessuch as ammonium sulfite, magnesium sulfite or potassium sulfite may also be used. A suitable treating solution comprises from about 1 -l0 percent by weight of sodium carbonate and from about 1 percent by weight of sodium sulfite, based on the dry weight of the kenaf. It has been found that sodium hydroxide may not be substituted for sodium carbonate in the practice of this invention since sheets made from a pulp treated with a sulfite solution containing sodium hydroxide may be dark colored, hard and tinny rather than soft and bulky as are sheets obtained from kenaf treated in accordance with this invention. The treatment of kenaf according to this invention softens and plasticizes the wood, produces more fibrillation upon grinding and yields a groundwood fiber which bonds better in the sheet.

The treatment may be accomplished by soaking the kenaf in a solution of the dilute alkaline sulfite solution. After soaking, it is preferred to compress the kenaf, such as in a screw extruder, to reduce the amount of occluded water and/or sulfite solution to a relatively low and uniform level and to crush the fibrous material. This also compresses the bulky cellulosic material, making it a more suitable feed to the refiner. The pressed, squeezed material expands as it emerges from the compression zone. At this point, it may be rewet with water or sulfite solution. The sulfite solution may also be applied to the kenaf after is emerges from the compression zone-i.e., the initial soaking of kenaf in the sulfite solution may be omitted.

The treated kenaf is then fed into a disc refiner of a type well-known in the art wherein it is refined to produce a groundwood pulp. During the refining it is important to fibrillate the kenaf as much as possible and to minimize chop. Significantly, less power is required to grind the kenaf than is needed to produce conventional mechanical pulp, such as from cotton wood. Water may be metered to the refiner to give controlled consistency in the refiner.

The pulp obtained in accordance with the practice of this invention compares favorably with presently used groundwood, obtained from wood. The alkaline sulfite treatment of the kenaf enhances fibrillation and reduces chop during the grinding operation. The pulp is high in freeness, fiber length, tear strength and mullen strength. It also has high bulk, resulting in lower sheet density. The pulp possesses good brightness and good opacity, scatter coefiiceint and absorption coefficient at equivalent brightness. The pulp may be bleached according to standard techniques, as with a solution of Na,0, to further increase the brightness. The outer bast fibers of kenaf are about as long as those of pine and have the small diameter of hardwood fibers. These fibers, which comprise 15 percent to 30 percent by weight of the stalk, have a high +20 mesh screen classification. The woody stem of kenaf, which accounts for about 70 percent by weight of the stalk weight, is made up of fibers which are shorter than hardwood but which are about the diameter of pine fibers. This results in a unique combination in pulp made from kenaf, the bast fibers contributing strength and the woody stem fibers contributing opacity and scatter coefficient.

Pulp prepared in accordance with this invention may be made into paper by conventional techniques.

The following examples illustrate the best modes contemplated for carrying out this invention. In these examples, all percentages and parts are by weight.

EXAMPLE 1 Kenaf which had been frost-killed was dried, aged and weathered in the field on the stalk for 3 months. It was then forage-chopped to about 3 inches in length. The chopped material was further stored in a large pile for about 7 months. The skin layer on the chopped stalks had darkened and contained a large number of dark specks. The chopped kenaf parts) was then screened on a iii-inch mesh screen to remove about 3.7 percent of dirt and extraneous material. The screened kenaf (96.3 parts) was soaked in water under ambient condition to equalize moisture. The water soak also removed some water soluble material from the kenaf. The soaking water was drained away and the kenaf (95.7 parts) was passed to a screw extruder wherein it was compressed to a solids content of 50 percent to 60 percent. During the pressing operation, 3.3 parts of solids in the liquid juice were removed. After pressing, the kenaf was mixed with an aqueous solution containing about 10 parts each of Na,COX, and Na, So; based upon the weight of the kenaf. The treating solution was added continuously to the kenaf emerging from the press. The

contact time with the treating solution was about minutes. The press was operated at a rate of 700-1 ,000 lbs. of dry kenaf per hour. The kenaf emerging from the press (1 12.5 parts, including occluded chemical) was passed to another press. This operation resulted in the removal of 13.5 parts of solids in the effluent. The kenaf emerging from the press was reduced to pulp by grinding in a double-disc Bauer refiner, in two passes or refining steps.

In the refining step, the fibrous material is introduced by a screw feeder through the center of one of a pair of counter rotation discs in an attrition mill. The material is reduced to a fibrous mass in the process of working its way outwardly between the attrition mill discs at their periphery. After the first pass through the mill, the product is collected and put through the mill a second time.

The pulp was thoroughly washed on a cloth filter and the filtrate (10.2 parts of solids) was discarded. After washing, the pulp (88.8 parts) was divided into two portions. One portion was bleached with a 2.5 percent Na,0, solution, based on the dry weight of the kenaf, the other portion with 5.0 percent Na,O The brightness of the pulp bleached with 2.5 percent Na,0 was 66.2 and that of the pulp bleached with 5.0 percent Na,0 was 70.9. In the case of the bleach with 2.5 percent Na,0 the total amount of bleached pulp obtained was 83.4 parts. Various physical and optical tests were made on the portion of the pulp which had been bleached with 2.5 percent Na,O and on sheets obtained from the pulp and the results are set forth in table 1.

For purpose of comparison, the above procedure was repeated except that the weak alkaline sulfite treatment was omitted. Physical and optical tests were also made on this pulp, and the results are set forth in table 1. The kenaf which had not been pretreated with sulfite had so much chop or comminution and so little fibrillation that considerable difficulty was experienced in forming sheets therefrom.

EXAMPLE 2 The procedure of example 1 was repeated except that the kenaf used was prepared as follows:

A chop of kenaf was cut while still green and when it had almost reached maturity. It was chopped to 3-inch lengths and dried with forced hot air to prevent fermentation and spoilage. The chopped kenaf was water soaked, pressed, treated with mild alkaline sulfite converted to a pulp and bleached as described in example 1. Physical and optical tests were made on the pulp and on sheets formed therefrom and the results are set forth in table 1.

In the following table, the properties were determined on pulp which had been bleached with 2.5 percent Na, 0

TABLE 1 Pulp 01 Ex. 1 Pulp of Ex. 2

Non- Nonsulfite Sulfite sulfite Sulfite treated treated, treated, treated percent percent percent percent Yield of bleached pulp based on starting kenaf 77. 4 83. 3 79. 9 92. 0 Freeness 0.8., c 69 160 177 134 69 58 56 62 218 226 261. 278 56 66 64 71 Opacity (40 lbs.) 96 88 87 Absorption coefficient (K.

1000 9. 4 2. 7 2. 4 1. 8 Scatter coefficient 9.6 8. 8 8. 5 7. 6

1n the above table, brightness is measured as the percent reflectivity compared to magnesium oxide and opacity is a percentage ratio of reflectivity of a single sheet of paper bafkfd by a black body and a white body, respectively.

c mm:

1. A process for the preparation of a groundwood pulp which comprises treating a dicotyledonous plant material at about atmospheric pressure and ambient temperature with an aqueous solution containing from 1 to 10 percent by weight of an ammonium, alkali metal or alkaline earth metal sulfite and from 1 to 10 percent by weight of sodium carbonate, said solution having a pH of from about 7 to 11.5, for from 1 to 30 minutes, and thereafter mechanically refining said treated material to convert it to a pulp.

2. The process of claim 1 wherein said solution has a pH of from about 10 to 11.

3. The process of claim 1 wherein said dicotyledonous plant is chopped kenaf.

' 4. The process of claim 3 wherein said chopped kenaf comprises pieces about %to 5 inches long.

5. The process of claim 3 wherein said aqueous treating solution comprises from about 1 to 10 percent by weight of Na, C0 and from about 1 to 10 percent by weight of Na So based on the dry weight of the kenaf.

6. The process of claim 5 wherein the pieces of kenaf are soaked in said solution and the treated kenaf is subsequently compressed.

7. The process of claim 5 wherein said pieces of kenaf are compressed and then are treated with said solution.

it l i 

2. The process of claim 1 wherein said solution has a pH of from about 10 to
 11. 3. The process of claim 1 wherein said dicotyledonous plant is chopped kenaf.
 4. The process of claim 3 wherein said chopped kenaf comprises pieces about 1/4 to 5 inches long.
 5. The process of claim 3 wherein said aqueous treating solution comprises from about 1 to 10 percent by weight of Na2CO3 and from about 1 to 10 percent by weight of Na2SO3, based on the dry weight of the kenaf.
 6. The process of claim 5 wherein the pieces of kenaf are soaked in said solution and the treated kenaf is subsequently compressed.
 7. The process of claim 5 wherein said pieces of kenaf are compressed and then are treated with said solution. 